1. Field of the Invention
The present invention relates to a contact-type image sensor used for reading an image on an object to be read. Further, the present invention relates to a contact-type image sensor wherein a sheet as an object to be read, coming into contact with a linear reading region, is reciprocally movable in a secondary scanning direction.
2. Description of the Related Art
As is well known, a copying machine and a scanner is used as an apparatus having a function of reading an image (including characters and symbols). Such an apparatus generally has an image sensor with a linear reading region.
FIG. 6 illustrates a typical structure of an image sensor used in the apparatus. The image sensor 100 which is a contact-type image sensor, is provided with a linear reading region 10 of a predetermined length. As shown in FIG. 7, the linear reading region 10 is provided on an upper surface 2a of a cover glass 2 mounted on an upper portion of a case 101. The image sensor 100 can read an image on the surface of the sheet P as an object to be read with the structure in which the sheet P moves while coming into contact with the linear reading region 10.
The sensor 100 is placed, for example, in a transfer base 109. The sheet P is transferred in a first direction d1 (a forward direction). The sensor 100, as shown in FIG. 7, is provided with a platen roller 8 pressing the sheet P against the linear reading region 10. In the sensor 100, the side wall 101a of the case 101 which is placed upstream in the forward direction projects above an upper surface 2a of the cover glass 2, whereas the downstream side wall 101b is arranged below the upper surface 2a of the cover glass 2.
In operation, the sheet P, moving toward the sensor 100 on the transfer base 109, abuts the side wall 101a. Consequently, the sheet P is slightly lifted by an inclined slope 101a1. Coming adjacent the linear reading region 10, the sheet P is pressed against the linear reading region 10 by the rotating platen roller 8. Thus, an image on the surface of the sheet P can be read successively. After passing by the linear reading region 10, the sheet P is transferred from the cover glass 2 onto the transfer base 109.
In this way, the sheet P's movement without touching anything but the reading region 10 may reduce the friction caused by transferring and the generation of static electricity caused by the friction. This may increase the transfer speed of the sheet P and may avoid the sheet P's deviation from the transfer path.
When the sensor 100 is used for reading the images on both sides of the sheet P, it is necessary for the sheet P to be turned over and to be transferred in a backward direction d2 which is reverse of the forward direction d1. Under such circumstances, in the sensor 100 with the structure as shown in FIGS. 6 and 7, the sheet P is prevented from moving in the backward direction d2 by an edge 2b of the cover glass 2 and an inside face 101a′ of the side wall 101a of the case 101. This may bend or tear the sheet P, and may prevent the images on both sides of the sheet P from being properly read.